Recently, in accordance with miniaturization of a semiconductor device, a method is needed, that is capable of forming a pattern having a dimension which exceeds an exposure resolution limit in lithography method.
As one example of the method, a method is known, that includes that sidewall patterns on side surfaces of a resist pattern (core material) are formed and a workpiece film which underlies is etched by using the sidewall patterns as a mask after the core material is eliminated. This method is, for example, disclosed in JP-A-1991(H03)-270227.
The above-mentioned conventional method includes that a bottom resist layer, an interlayer (spin on glass film), an upper layer resist pattern (core material) are formed in this order, and then a silicon nitride film (sidewall pattern) is formed in both of the sidewalls of the upper layer resist pattern, and the upper layer resist pattern is eliminated by development or ashing, and then the interlayer is etched by an etchant while using the silicon nitride film as a mask, and the bottom resist layer is anisotropically-etched by using oxygen plasma. Consequently, a microscopic pattern having a three-layer structure is formed, the three-layer structure including the bottom resist layer, the interlayer, and silicon nitride film.